This invention relates to fire extinguishing systems for oil storage tanks, especially floating roof tanks.
The storage of oil and other combustibles within large tanks has traditionally involved significant safety hazards due in part to the possibility of fires and explosions produced by vapor accumulating between the oil and the tank roof. These dangers have been greatly reduced by the use of floating roof tanks in which the roof is permitted to float with changing oil levels to minimize the voids which can occur therebetween. A flexible seal is disposed between the outer rim of the roof and the side of the tank. Such floating roof tanks, however, are not completely danger-free. Upon occasion, fires have broken out along the rim seal where vapors have collected. If allowed to burn uncontrolled, these fires can produce serious catastrophes.
Systems have been proposed which are intended to detect and extinguish fires on floating roof tanks. See, for example, U.S. DeBoer Pat. No. 3,896,881, issued July 29, 1975, and U.S. McCulloch Pat. No. 3,741,309, issued June 26, 1973 for systems of this type. It is common to arrange a series of sprayers around the periphery of the tank roof. The sprayers are connected to a continually pressurized fire extinguishing agent. A temperature sensitive element on each sprayer reacts to high temperature conditions to open its associated sprayer, causing agent to be emitted. A system of this type is subject to certain drawbacks. For one thing, systems in which the agent is continually pressurized generally require special equipment for refilling the agent containers. Thus, added expense and complexity is involved in maintaining the system once installed.
A further problem is produced by the nature of rim seal fires which can occur. Often, such fires begin as very low order fires depending upon wind conditions, the type of combustible being stored, and other factors. A system in which only the sprayer closest to the fire is activated can be fooled by a migrating fire which does not activate other sprayers until all of the extinguishing agent has been depleted through the initially activated sprayer. A system has been proposed in which all of the sprayers around the entire rim periphery are activated simultaneously when a fire is sensed, but this is costly and leaves the entire rim unprotected after the extinguishing has been depleted.
An additional area of concern involves system integrity. A system which sits unactivated for long periods can develop leaks, clogs, etc. which may go unnoticed. Of course, the extinguishing agent can be expelled occasionally to test the system, but this involves considerable expense.
It would also be desirable to provide a system which can be securely fastened to the roof so as to minimize potential dangers due to high winds and to guard against damage by careless workers who may be active in the area of the system.
It is, therefore, an object of the present invention to eliminate or at least significantly alleviate problems of this nature.
It is another object of the invention to provide a fire extinguishing system for floating roof tanks which can be easily maintained without the need for special equipment.
It is a further object of the invention to provide a fire extinguishing system for floating roof tanks which effectively guards against migrating, low order rim seal fires.
It is still another object of the invention to provide a fire extinguishing system for floating roof tanks which is securely mounted in a manner providing optimum component protection.
It is yet another object of the invention to provide a fire extinguishing system for floating roof tanks which can be periodically tested in an effective yet economical manner.